1. FIELD OF THE INVENTION
This invention relates to clamping devices for use in regulating fluid flow through plastic tubing and more particularly to such a device employing a roller wheel which is adjusted along a generally longitudinal axis relative to an opposing clamping surface, to adjust and set the fluid flow rate through the tubing.
2. DESCRIPTION OF THE PRIOR ART
In my U.S. Pat. Nos. RE 31,584, 4,013,263, 4,047,694 and 4,725,037, clamping devices are described for regulating fluid flow through plastic tubing which are particularly useful in the administration of parenteral fluids. The clamps of my aforementioned patents have the advantage in that creep or cold flow of the plastic material of the tubing is greatly reduced to provide a more constant rate of flow of the parenteral solution diminishing the need for later adjustment once an initial setting has been made. In my U.S. Pat. Nos. 4,013,263, 4,047,694 and 4,725,037 clamps are described in which an improvement in the constancy of the flow rate is achieved by employing raised portions formed in the clamping surface which portions are separated from each other by discrete valley portions so as to pinch or grip the tubing in discrete locations or intervals, thereby substantially lessening creep of the plastic and minimizing flow rate changes once the clamp has been set for the desired flow rate. In the preferred embodiments of these patents, the raised portions are in the form of long ridges which are spaced from each other in an optimum manner for creep reduction.
Generally, softer tubing acts in a more compliant manner when combined with a pinch clamp because such tubing will more readily conform to the new configuration imposed by the clamp. Harder or stiffer tubing has the attractive feature of being resistant to kinking when coiled or bent as is the case when packaged. Kinking may be defined as a permanent deformation assumed by a tube due to a radical and/or long term new configuration imposed to cause the tube to assume a new configuration with a radius of curvature below some critical value. Plastic tubing when used as a disposable assembly for intravenous feeding is often packaged in the shape of a compact oblong coil. The coil is approximately 8 inches long and 3 inches wide while the tube is some 70 inches long. If the coil radius is too small, the tube will tend to kink, thus compromising the tube's ability to transfer fluids when later put to use. Large radius coils are undesirable because the coils occupy too large a volume when being stored prior to use. Thus, stiffer tubing is considered as a means to make possible a compact tube coil package. Increased stiffness may be achieved by a thicker wall cross section or by increasing the hardness of the tubing material, or both.
A thicker walled tubing usually helps to reduce the tendency for the tube to kink.
When utilizing a generally parallel acting clamp, at any given tubing cross section, a portion of the tubing must be fully pinched shut as well as being tightly confined. Utilizing a thicker wall or stiffer tubing tends to make the problem of pinching and confining more difficult by requiring the pinch clamp to be stronger and larger in size so as to provide additional force and leverage, respectively. Furthermore, the small raised elements on the housing clamping surface such as those described in U.S. Pat. No. 4,013,353 may be less effective with tubing having stiffer and/or thicker walls.
Furthermore, for the case of stiffer and/or thicker walled tubing, introduction of the raised elements tends to have an effect upon the size of the lumen formed, generally tending to increase its size, (other things being equal).
In one series of controlled experiments, it was observed that the effective flow cross section of the formed lumens was considerably greater when raised elements were introduced and all other factors were unchanged. This difference was even more dramatic when tubing which was both stiffer and having a thicker wall was used in the study. In that application, the market required that this type of stiff, thicker walled tubing be used and would not permit the introduction of a thinner walled softer tubing.
In a second controlled study, it was observed that when the raised elements were located closer to the relief section of the clamping surface of the clamp housing, the effective lumen cross section was larger, than when the raised element nearest the relief section was more distant.
Having the raised element more distant from the relief section of the clamping surface reduced the size of the lumen, but this did not offer the full benefit of the raised elements (tug resistance and improved flow control).